Airplane



Marh 22, 1932. T, BERBECK 4 1,850,786

AIRFLANE Filed Oct. 2B, 1950 im? JNM/mba al Mm/mw akamu# Patented Mar.1932 i' lasen@ mun Bananen, or mrmonn,

Antrim Application med ottcber as, 19am serial No. 491,790.

This application is a continuation'in part of my copending applicationSerial No. 422,- 639, iled January 22, 1930.

This invention relates to improvements in 5. airplanes and moreparticularly has reference creased wing area. However, these eXpedi-.

ents are limited by the size of thel wings which y are capable of beingused. Other methods '-f' have proposed a wing construction which allowsthe camber and the wing area to be zaitere at win. whatl this lattertyp@J 0f vconstruction is correct in theory, it'is neverthelessimpractical because of the many mechanical parts required by it.

' Besides these practices mentioned above, attempts have been made toincrease the lifting power of an airfoil by increasing the air currentvelocity over the top Surface. Along 3" these lines the slotted wing hashad considerable success, but as yet it is not suitable in al1-mstances. Also among this latter type of s methods for increasing thelift of airfoils is the use of blowers adapted to direct a stream vofair over the upper surface of the plane.

land in sm-all spaces, at relatively low spec use of the vinteriorsurfaces of an'airfoil to increase the lifting eiiect. l

Yet another object of the invention is to circulate a'current of air.within theinterior of. an l.a-irfoiL-the air current entering and 65leaving the airfoil at its bottom surface.

In addition to the above objects, the present invention comtemplates theconstruction of alrplane wings so *that an airplane my s 60 and with amaximum factor of safety. i

Still another object of this` invention is the provision ofi-a hollow`airfoil having a rotatable ller mounted within openings formed init elower surface thereof, and hav-v 65- ing openings or'slots formed in theupper surfacethereof. p A still further object ofv this invention isAvthe-association with the wings ofa'n airplane of means operable forincreasing'the lift effect I0 'of the airfoils during descent of theairplane..l

With these and other objects in view, which may be incident to myimprovements, the in; vention consists in the parts and combinations tobe hereinafter set forth and claimed, with 'l5 the understanding thatthe several necessary elements comprising my invention may' be varied inconstruction, proportions and ar rangement without departing from thespirit and scope of the appended claims.

The present invention comprehends a method and apparatus for increasingthe lift factor of airfils. One method of practically effeeting theconcept of the invention is the provision of an arfoil having an openingformed These have been unsuccessful dueto the fact /if its lower surfaceand means upon theplane of a small increase of velocity obtained for thegreat amount of weight added to the plane. It is the ma] or object ofthis invention to provide a method forincreasing the lift of airfoilsand means for cari-tying the same into effect which lack the inherentdefects of methods and constructions now in present practice.

Y Y .An equally important object of the invention is to create a currentof air which is directed around the airfo'il from its bottom surfaceupwardly and over the top surface th'erely understood, I have shown, inthe accom-l 5 Another object of the inventionis to make with which theairfoil is associated for rotating vane mechanism positioned within theOpemnss- It is also within the concept of the present invention to soposition openings in the hollow wingsor airfoil structures equipped withthe rotating impellers, that the impellers may .be caused to rotate dueto the passage of air currents through the wings'or airfoil sections.Y Y

In 'order to make my invention more clearpanying drawings, means forcarrying h IAfri-. :N'rf orales i 1 .the shafts. 1l maybe employed. Thisconstruct1onit will be observed, provides a set foil ofthe same intopractical eiect without limiting the improvements in their usefulapplications to the particular constructions which, for the purpose ofexplanation, have been made the subject of illustration.

In the drawings there is illustrated a diagrammatic representation ofthe application of the present invention in which:

Figure 1 is a horizontal bottom view of an airplane showing theconstruction forming this invention embodied in the wing or airplane.

Figure 2 1s a partial vertical sectional view of an. airplane providedwith an auxiliary airfoil having the impeller structure embodiedthe-rein. a

Figure 3 is a top .plan view of one form of airfoil constructed inaccordance with the present invention, being taken on line 23e-,3 ofFigure 2.

Figure t is a vertical sectional view taken on line 4-4 of Figure 2. v

Figure 5 is a view similar to Figure 3, illustrating a modification ofthe present inven` tion. 1

Figure 6 is a vertical'sectional view of a still further'modification ofthe present invention. v

There is shown in Figure 1 an airplane having a fuselage 1 and a wing orairfoil 2. The airfoil 2 is providedwith the usual Vailerons B-While'thetail of the fuselage has mounted in suitable bearings 12 which may befixed to the ribs 13 of the airfoil.

However, any other suitable bearing support for of vane elements. oneach side ofthe fuselage or on each semi-span. y For the purpose ofprovidin a commercial structure, the openings have een shown as formedwithin -a plate like structure v9. A plate 9 is mounted upon eachsemi-span of the airfoil and is covered with the usual surfacingmaterial. j It will be appreciated that by this feature, the plate maybe made espeorally and set in or recessed into the lower wing surface sothat it is flush thereto. Of

course, if -it is desired, the openings 9 may be cut directly into thelower wing surface and the plate 9 dispensed with.

It is to be-noted that each vane .element is of a size substantiallyequal to an opening '9,

.and is so designed that it may freely rotate unit 14, shown by thedotted lines in Figure 1,

is connected to the shafts 11. In order to prevent the drawings frombecoming highly complicated by reason of unnecessary detail, the shafts11, provided -for each set of vane elements, have been shown as directlyconnected to the power unit 14. It is to be understood, however, that asuitable clutch arrangement between each of these shafts and the powersource may be employed so that either or both shafts 11 may beunconpledfrom the power unit and the latter may be. actuated without rotating thevane elements. Also itv is to be understood that although I have shown aseparate power i unit for rotating the vane elements, b suitand theseparate power source 14 eliminated.

While the construction details have shown each set of vane elements asbeing positioned upon the wing so that the axis of the shaft upon whichthe vanes are mounted is parallel to the longitudinal axis of theairfoil, it will be appreclated that each set of vanes may be sopositioned that the axis of its shaft is perpendicular to thelongitudinal axis of the airfoil or it may be angularly disposedthereto. In these lattens events, each set of vane elements could bedriven b a separate 'power unit or by means of suita le gearing could beconnected to a centralized unit, such as that shown at.14, or to theprime mover rotating the propeller. l

As it Will hereinafter become apparent, the invention isv in no wayslimited to the number of vane elements, it bein within the scope of theinvention to emp oy one such vane element of greatly enlarged area oneach semi-wing span. Neither are the vane elements limited in shape,area or their position with respect to eitherV the longitudinal or thetransverse axis of the a'irfoil. For instance. the vanes or impellersmay be of any desired shape, circular, square, etc.,and may be locatedin any portion of the wing structure, in any position depending upon thetype of airplane andthe results to be obtained. Moreover, while I haveshown the invention as embodied in' a monoplane, it will be appreciatedby those skilled in the art, that it may be embodied in othertypes ofplane as well, for example, a biplane or triplane. It will also becomeapparent that the invention is not limited to any particular type ofairfoil section, as it may be equally well employed with any airfoilsection design.

` in allowing a short distance take-olf and a relativel low landingspeed and small space for landing a plane. As is well known, lthecreation of lift in an airfoi-l is due tothe pressure differentialexisting between the pressure upon the upper surface of the airfoil andthe pressure upon its lower surface. The pressure upon the upper surfaceis negative in value, or a suction effect, while that upon the lowersurface is positive with respect to the atmospheric pressure.

The best explan 'on of the values of these areas of high and lowpressure about the airfoil may be obtained y the application of some ofthe theorems of hydro-dynamics, par

ticularly Bernoulli-s. As an airfoil is moved forwardly, there is alwaysair ahead of it which has not been disturbed by the passa e ofthe-airfoiL This air is referred to as t e air stream and as it reaches theairfoil divides, part of it going over the upper airfoil surface andpart of it going below the airfoil Surface. Bernoullis theorem would,indicate that the Aair nearest the 'upper surface of the wing,

which is at a pressure less than that in the air at a distance from thewing, has a velocity whichis higher than that in the air stream .at adistance from the wing. On the other. .hand the velocity of the airnearest the lower wing surface is less than that of the air f stream. Byfurther application of this theorem, it will be appreciated that thepressure of the air passing over the airfoil is less than l is forinedalong thetrailing edge a succession of small vortices which break oil`and remain in the air as the airfoil passes. These trailing edgevortices, itis assumed, set upa counter circulation around the wingwhich increases in strength until the ilow olf the trailing edge issmooth. This effect takes place within a comparatively smallamount oftime and the full lift of the airfoil is developed very quickly afterthe airfoil begins to move.

Assuming that an airfoil is positioned so that its leading edge ispointed towards the left as shown in Figure 2, such a countercirculation of air, as that described above, is directed in a clockwisedirection.- Now this counter air current, as it passes over the lowersurface of the airfoil, will be opposite in direction tothe air'ilowingover the lower surface caused by the movement of the airfoil,

.and hence will decrease its velocity with a consequentpressure rise. Othe other hand,

as the counter current of air passes around the leading edge and overthe upper surface of the air oil, its direction'will be coincident withthat of the air flowing over lthis surface, and it will tend to add toor build up the velocity of this air with a consequent decrease inpressure upon the upper surface. Y

It is the purpose of this invention, among other objects as will bepointed out, to make use of this theory as outlined above and to buildup vor strengthen the counter air current. In order to accom lish this,the rotatable vanes such as have geen shown, are employed. By rotatingthese vanes at a suitable speed, an additional counter current aidingthat already mentioned will be generated, the vanes being rotated in aclockwise direction as shown in Figure 2.

a As it will be noted in Figure 2, each vane element 10 is formed of ablade 10a and a blade 10b. In explanation of the operation of thedevice, the revolution of one of the blades will be traced. Assume thatthe blade 10a as shown in Fi re 2, is in such position that it is flushwit the right hand side of the opening 9. l

Now as the blade 10a .is rotated from the sition described, it movesdownwardly and its front face, that is, the face adjacent to the leadingedge ofthe airfoil, is in contact with the air flowingover the lowerairfoilsurface. Besides increasing the pressure upon the lower surface,this results in deflecting some of lthis air stream into the interior ofthe ail-foil and moreover creates a current or flow of air through theairfoil itself. Asis well known, centrifugal force will cause thedeflected and the generated air, caused by the rotation-of the blade, tobe given a considerable velocity as the blade 10a moves towards theleading edge and within the airfoil. Th1s circulation of air within theair-foil is continued, and because of the shape of the air- .side of theopening 9 asthc blade 10a again assumes its initial position.

It will be observed that the direction of this aircurrent flowingthrough the airfoil is clockwise and the same as the counter current ofair set up by the trailing edg vortices. As this air is ejected from therig t of the openings 9, it is commngled with the circulatory countercurrent flowing around the airfoil andthe velocity of the latteris builtup due to the addition of the air expelled from within the airfoil asthe blade descends.

. The counter circulatory current of air flowing over the lower surfaceof the airfoil, it will be appreciated, has had its velocityconsiderably increased and as this meets the air stream flowing over thelower surface in an opposite direction to it, the velocity of the latterwill be decreased. This results in an increase of `pressure upon theunderside of the airfoil which exceeds the amount possible to beattained without the use of the-vane elements.

Now as this circulatory counter current of increased velocity passesaround the leading ed e of the airfoil and over its upper surface, it isdirected in a path substantially coincident with the air stream flowingover the upper surface, and the velocity of this air stream is built upwith a consequent greater restriction of pressure on the upper surface.Hence it will become apparent that by the use of the vane elements, asdescribed, the' pressure upon the lower surface of the airfoil will beconsiderably increased, while that u on the. upper surface will bedecreased. s it is a parent, the result of this enlarged pressureiferential will create an increased lift factor. I v i Besides eneratingan increased counter current havlng a circulatory flow around theairfoil, the invention intends to make use of the inner surfaces of theairfoil as well as the outer surfaces for lifting effects. It has a1-read lbeen mentioned that an air current of considerable velocit iscirculated through the interior of the airfoil due to the rotation ofthe blades forming each vane element. The velocity and pressure of thisair 1s not only due to that deflected from the lower air stream byreason of it impinging against each blade as it starts to ascen into the1nterior of the airfoil, but is also caused by air current generated bythe `rotation ofl the vane elements. It has been conclusively roved thatthe upper surface of an airfoil 1s within an area of negative pressureand it will hence be realized that the ressure created upon the interiorof this sur ace, due to-the vane elements, will be opposite in slgn andsucient to cause a considerable pressure diferential'to exist betweenthe upper exterior surface of the airfoil and the upper interior surfaceof the airfoil. As a conseuence, an increased lift effect is providedfor t e airfoil and' the'interior surface as well as the exteriorsurface will be utilized.

It has been mentioned that the blade elements are rotated at a suitablespeed. Such a speed is dependent upon such factors as the size of theairfoil, the area of the vanes, and also upon their number. While thevanes have been disclosed as being circular in shape, it will beappreciated that any other metrical shape desired may be given to t emwithout departing from the spirit of the invention or the scope of theappended claims. Likewise,.it will be appreciated that the invention isnot limited to the number of blades formed upon each blade element. Forinstance, a single vane may be employed.

It will be appreciated that the invention is of great advantage inincreasing the lift of an airplane, being particularly useful in takingolf and landing. The power unit '14: is actuated so as to rotate thevane elements as described, with the result that a counter circulatoryairflow and an airflow within the interior of the airfoil are set u Thiswill greatly increase the lift coe cient at all angles of attack, andhence Will allow the plane to be taken olf Within a relatively smallspace and to be landed at relatively low spee and within a small area.

While the plane is flying and it is no longer desired to rotate the vaneelements, the actuation of the power unit is arrested and the shafts 11may be unclutched therefrom. It should be -noted that either or bothsets'of vane elements may be unclutched from the power unit and henceeither or both-'of them may be driven as desired. v If desired, theimpellers may be locked in a position so as to maintain the same flushwith the lower surface of the win The pressure of the air stream passingelow'the lower Wing surfaces will act on the vanes in closed to anyconventional wing. T he reason for constructing the vane elements sothat when 'they are in closed position they are flush with the lowersurface will now become apparent. By this construction, parasiticresistance due to their projection below the airfoil surface isposition, and thecairfoil will function similar prevented. Although thebearings 14 have been shown as extending below the lower wing surface,it will be appreciated that these may be so constructed as to besubstantially flush therewith. I

While the advantages derived from this construction have been outlinedin connection with the landing and the taking oli' of airplanes, and areof particularv value in these instances, it will be understood that theywill be effective while' the plane is flyingin'the air. Such a use ofthe vane element is of advantage in pulling an airplane out of a stall,a dive, or a spin. Y v

As is well known,4there exists upon the wing tips of an airplane, awhirl or vortex, which creates an uneven distribution of pressure overthe wing surfac-es near the tips, increases the drag of the airfoil .andin general decreases the stability of the airplane. 'Attempts have beenmade to ameliorate this con-l dition by varying the shape of the wingtip. f

As a consquence, it has been discovered that an'elliptical tipped Winggives the best results, but these are not highly satisfactory. Bysuitably ositioning 'a series of vane elements upon t e wing tips,either as shown 'or' so that the axis of rotation `is perpendicular tothe longitudinal plane axis or an ularly disposed thereto, these aircurrents owin'g over and under the Wing tips could be straightenedoutand hence an even distribution of the pressure over ,this areawouldlbe procured with a decrease in the drag of the airfoil. Y

In Figure 2, the invention is embodied in an auxiliary airfoil adaptedto be mounted below the main airoil 4of an a' lane, one such auxiliaryairfoil beingposltioned on each semispan; Here a cabin' plane having afuselage 1 and an airfoil 2 is rovided with an auxiliary ail-foil 15.The selagepf thxplane is provided with the usual wind shielandvsupporting structure therefor as indicated by the reference numeral16.

Y Each auxiliary wing is provided with a set of vane elements such asthat described. These vane elements are actuated similarly to thoseshown in Figure 1. Under each semispan ofV theA main airfoil 2theauxiliary wing is mounted by means of suitable sup Y ports or braces17 which may be secured to the main ail-foil 2' or to the fuselageitself to both of these structures. Each auxiliary airfoil is positionedat such a distance belowthe main airfoil 2.".thatg substantially nointerference with the air cur.-

' rent vpassing under the lower surface of the airfoil 2 is created. Asis well known, such a distance is dependent uponthe gap/cord ratiogiving the best results and it may be decreedb 'tively staggering theairfoils.

In suc Pcstruction, it will 'be appreciatedthatthe -main airfoil 2'mayalso be' provided with vane elements such as shown u in connection withthe airfoil 2 in Figures l and 3. Y By -the structure employed in Figure2, construction of biplanes or triplanes having .a smaller wing area ispermitted. Biplane. and triplane construction is employed where l Y itfound impractical, because ofthewing area required, to embody .anairplane odesi ina vmonoplane design. By the use oft e vxiuailiaryairfoils, it will be appreciatedthat the win area of such a plane andconse- "quently its weight, could be considerably reum 2, it mul beappa-ent um both the main "duced while its lift factor' would be greatlyincreased. In'the construction shown in Fig.-

- 2 and the auxiliarv wing 15 will function in a manner similar-to thatdescribed in the embodiment of 'the invention disclosed in Figure 1.

v Units such as an auxiliary airfoil 15 employing the present inventionmay be positioned at various points on the plane where an increased liftisdesirable.

I have found that` .the present invention may be operated to increasethe lift eiiect o an airplane while descending without em-Vployiiig-powerato eiect rotation of the imvpellenelements10.v In` thedrawings, I have Y shown a form o'f invention in which the upper surface'of the wing section 15, equipped with f the rotatable impellers 10, isprovided with Y a plurality of openings 18,` so positioned in the uppersurface of the airfoil as to eiiect 'rotation of the impellers 10 whenthey are torotate'and 'whenthe stream of air factorily than the formgures and vice versa.

ilowing through the wings or auxilia airoil sections 15. If desired, asshown elillearly in Figure .4, the openings 18 may be provided withsuitable closures 19 carried by an actuating member 20'and controlled bythe lever 21 for opening or closing the openings 18 any desired amount.

It will be appreiziated that in order to effect the most eicientoperation of the impellers l0 when they are not rotated by a source ofpower, they should be disconnected from the engine or other source Vofpower. In Figure 4, I have shown one means of accomplishing thispurpose. In that ligure, the impellers 10 are 'carried on suitable hubs'22, rotatably mounted. on the shaft 11. The hubs 27 are provided withsplined sockets 23, into which may be moved an enlarged portion 24 ofshaft A 11, provided with splines adapted to cooperate with those in thesocket 23 to cause theI impellers 10 to rotate with the shaftlll Thuswhen it is desired to cause an airplane to descend without the use of asource ofA power for rotating the impellers 10, the lever 25 may beactuated to cause the shaft 11 carrying the enlargedesplined portions 24to become disengaged -,w1th the impellers 10, thereby-peren an airp aneequi pe wit t e res4 ent invention is descendiliig, there 'is apilow ofair through the wings which may be caused by a principle analogous tothat employed in the provision of thefso-called slotted wing. This.current of air will cause rotation of the impeller 10, and thisrotation of the .impeller will have a tendency to increase the lift eectof thejairfoil equipped with thesame in a Ymanner Y similar to thathereinbefore described. Inplaceof the location of a plurality of smallopenings in the upper surface of a wing section constructed inaccordance by varying the openings. Y

If desired. the nresentinvention may be further modified by locating theshaft 11 vlnitting the same to be freely rotated within Y more centrallywithinthe airfoil section as shown in Figure 6. In this figure, theshaft- 11 is positioned above the lower surface of the airfoil andtherebv will have a slightly In some instances, it will be found thatthis form of the invention will operate more satisf shown in the otherdifferent effect on the lift ofthe airtoil section.'

It may be possible that the lift effect lob tained by the presentinvention is due to the pressure created by centrifugal action of thevanes or impellers, which exerts a pressure upwardly against theinterior of the Wing surface and also in a general opposite direction.On the other hand, it may be possible that the invention operates on theprinciple emlployed in the so-called rotor ship.

l0 egardless of any theory of operation, ex-

periments have shown that an increased lift effect is obtained whenairfoils are constructed and operated as herein described.

.Having described the features and operation of the device, it will beappreciated from the foregoing description that I have provided a methodand means for greatly increasing the liftingpowers of airfoils. Suchconstruction as that disclosed will allow a 2 short distance take-offfor a plane and a relatively small landing area besides having manyother advantageous effects which result rolr: the benefit of increasingthe lift of air- While I have shown and described the preferredembodiment of my invention, I wish it to be understoodthat I do notconfine myself to the precise details of construction herein Yset forth,by way of illustration, as it is apparent that many changes andvariations i may be made therein, by' those skilled in the art, withoutdeparting from the spirit of the invention, or exceeding the scope ofthe appended claims. I

1. An airfoil having an ope lower surface, an openln in its up rsurface, an impeller rotatab y mount within the openin formed in thelower surface of the airfoi and closure means associated with theopening in the upper surfaceof the airfoil. 2. An airfoil havin anopening in its lower surface, an impel er rotatably mounted within saidopening, said airfoil having a slot in its upper surface adapted toincrease the lift effect of the airfoil, and a closure for said slot.

3. An airfoil having a plurality of openings formed in its lower surfaceand a plurality of impellers rotatably mounted within said openings,said airfoil also having openings 1n its upper surface adapted to directair streams through said airfoil to rotate the im llers and therebyincrease the lift effect o the airfoil and means for adjusting the sizeof the openings in the upper surface of the airfoil.

4. An airfoil having a plurality of openin formed in its lower surfaceand a plura ity of impellers rotatably mounted with in said openings,said airfoil also having a slot in its upper surface adapted to directair streams through said airfoil'to rotate the o c n ning 1n itsimpellers and thereby increase -the lift effect of the airfoil and meansassociated with the slot in the upper surface of the airfoil to con- 5.An airfoil having a plurality 'of open.v

ings formed in its lower surface, disl-like impellers rotatably mountedwithin ,said openings, each lof said impellers being so constructed thatwhen it is in a position to close the opening within which it ismounted, it will lie substantially fiush with the surfacing material ofthe airfoil, said airfoil also having an opening formed in its uppersurface adapted to cooperate with said impeller to effect a` variationin thelift of the airfoil.

6. An airfoil having a recess formed in its lower surface, a shaftextending through said recess, a disk-like im eller mounted upon saidshaft and positione within said recess, means detachably connected tosaid shaft'for rotating it and said impeller, and said airfoil alsohaving openings formed in the upper surface thereof adapted to cooperatewith the impeller to increase the lift effect of'said airfoil. i

7. An auxiliary airfoil forpan airplane adapted to be mounted below awing of said airplane, said auxiliary airfoil being provlded with aplurality of openings upon its lower surface, vane elements rotatablymounted within said openings, said vane elements bein so constructed asto lie substantiall ush withV the lower surface of said auxiliaryairfoil when the vane elements are in position to close said openings,said airfoil having an opening formed in the upper surface thereofadapted to cooperate with the vane elements to increase the lift effecton the airfoil.

8. In an airplane an auxiliary wing therefor adapted to be positionedbelow a main wing, said auxiliary wing having an airfoil section andprovided with an' opening upon its bottom surface, an impeller rotatablymounted within said opening, and power driven means upon the airplanefor rotating said impeller, said airfoil having 'an opening formed inthe upper surface thereof adapted to cooperate with the vane elements toincrease the lift effect on the airfoil and means associated with theopen- 'i'ngs in the upper surface of the airfoil for varying theeiective area thereof.

9. A wing for an airplane having an airfoil section of hollowconstruction covered with surfacing material, an opening formed in thebottom surface of the material, an impeller rotatably mounted withinsaid open ing, said material having o nings formed therein in the uppersurface t ereof, said last mentioned openings being so positioned as toeffect rotation of the impeller to increase Vthe lift et'ect of the Wingand means asso- @lated with the openings in the upper surface of theairfoil for varying the eective area thereof.

10. An airfoilof hollowconstruction covered with surfacing material,said material having an opening formed in the lower surface of the`airfoil, a shaft positioned within the airfoil a distance from thesurfacing material, an impeller mounted upon said shaft, and means ordetachably connecting said shaft with a source of power, said surfacingmaterial also having an opening formed in the upper portion of theairfoil adapted to eectl the iiow of a stream of air through the airfoiland rotate the im ller when disconnected from the source o power.

11. In an airplane ay luraliilof auxiliary airfoils therefor, sai a -aryairfoils adapted to be mounted below the main airfoil of said airplane,each of 'said auxiliary m airfoils being provided with a plurality ofopenings formed upon their bottom surface, vane elements rotatablymounted within each of said elemen, said airfoils having an openingformed in the upper surface thereof adapted to cooperate :with the vaneelements to increase the lift effect onrthe airfoil, and meansassociated with the openings in the upper surface of the airfoils forvarying the effective area thereof.

3 12.A An airfoil of hollow construction covered with surfacingmaterial, said material having an opening formed in the lower sur# faceof the airfoil, a shaft positioned within the airfoil a distance fromthe surfacing mau terial, an impeller mounted upon said shaft, and meansfor detachably connecting Vsaid shaft with a source of power, saidsurfacing material also having an opening formed in the upper portion ofthe airfoil adapted 4 to effect the flow of a stream of air through theairfoil and rotate the im ller when disconnected from the source opower, and meansv associated with the openings inthe upper surface ofthe airfoils for varying the e'ective area thereof.

In testimony whereof I aixm signature.

. TRIAN BE BECK.

